Motor assembly for housing a capacitor in a miniature brushed dc motor and method of making the same

ABSTRACT

A motor assembly for a direct current (DC) electric motor, including: a motor cover, a brush base, brush arms and a chip capacitor housed within a protective hollow space provided in the brush base. The brush arms are shaped to support or hold the capacitor within the hollow space and maintain a solderless electrical connection between the terminal ends of the capacitor and the brush arms. The capacitor filters electromagnetic noises in the motor input circuit.

TECHNICAL FIELD

Certain exemplary embodiments described herein relate generally tominiature, direct current (DC) electric motors used in motorized devicesincluding, for example, motorized toys, audio and video equipment, handtools and other electrical motor-driven devices, vehicles or appliances.More particularly, certain exemplary embodiments relate to an improveddesign and assembly method for using a chip capacitor in the inputcircuit of a miniature, DC electric motor to filter electromagneticnoises.

BACKGROUND AND SUMMARY

Typical miniature DC electric motors have a metallic cylindrical motorhousing formed of mild steel or the like and defining a hollow tubularsection and an integral bottom. One end of the motor housing is open toreceive a motor cover, which encloses the open end of the motor housing.The motor cover includes a brush arm holder that may comprise a separatebrush base, or the brush base may be an integral part of the motorcover. Within the motor housing are fixed a pair of opposite permanentmagnets, each of which has an arc shape to match the inner wall of thehousing. The magnets form between them a volume in the housing for arotor. The rotor typically includes a cylindrical armature coaxiallymounted on a rotor shaft. The rotor shaft extends through the oppositeends of the motor housing. Bearings may be used to rotatably support therotor shaft in the ends of the housing. For example, the bottom of themotor housing may have an integral flange, into which a bearing can bepress-fitted to support one end of the rotor shaft. The end cap may havea similar bearing structure. In this way, the rotor shaft is held incoaxial alignment with the motor housing.

The brush holder supports a pair of brush arms which provide anelectrical connection to an external electrical contact of the motor.The brush arms are generally strips of copper having a first end whichserves as the external electrical contact and an opposite, free end onwhich is mounted a brush. The brush arms are fixed to the periphery ofthe brush holder and are attached to opposite sides of the brush holder.The brushes located on the brush arms face each other at the axis of themotor. When inserted in the housing, the brushes are in slidable contactwith a commutator on the rotor shaft. The commutator provides anelectrical contact between the wiring of the armature and the brushes.The armature may include any suitable number of wire windings, such asthree windings. The external contacts of the brush arms provide DCcurrent through the brush arms to the brushes. The brushes provide DCcurrent to the commutator. The commutator provides DC current to thewindings in the armature. Electrical current input through the armaturecreates an alternating magnetic field within the housing that interactswith the magnetic field of the permanent magnets. This interaction ofmagnetic fields creates a force that rotates the rotor. This rotationdrives the rotor shaft to provide a mechanical rotational output powersource from the rotor. The rotor shaft extends through the bottom of thehousing to provide a mechanical power output to drive a gear box orother device. Exemplary miniature electric motors and particularcomponents thereof are shown in, for example, U.S. Pat. Nos. 6,528,922;6,717,322; 5,294,852; 5,010,264, the disclosures of which areincorporated by reference herein.

Such miniature electric motors can be and are used in a variety ofapplications, including, but not limited to, motorized toys, audio andvideo equipment, hand tools and other electrical motor-driven devices,vehicles or appliances. Miniature DC electric motors tend to be arelatively-low cost component of toys and other equipment. Accordingly,it will be appreciated that it is desirable to reduce the manufacturingcosts and complexity associated with making such motors. It is alsodesirable for various applications incorporating miniature electricmotors in a variety of exemplary scenarios to reduce unwantedelectromagnetic noises in the electrical input supplied to the motors,as one skilled in the art will appreciate from the description herein.

Shown in FIG. 1 is an example of a conventional DC electric motor brushbase and brush arms assembly 100 for attachment to motor cover 128 atbrush base attachment section 126 thereof. Assembly 100 includes a firstelongated metal strip forming brush arm 106, having a brush 114 on oneend and external electrical contact 118 (including soldering hole 110)on the other end, and a second elongated metal strip forming brush arm108, having brush 116 on one end and external electrical contact 120(including soldering hole 112) on the other end. Brush arms 106 and 108may comprise of any electrically conductive metal, but are typicallyfashioned from copper.

In a conventional assembly method, brush arms 106 and 108 are insertedinto opposite ends of brush base 104 at brush arm elbow sections 122 and124 to form brush base and brush arms assembly 100. FIG. 2 is asectional view of assembly 100 which shows brush arms 106 and 108inserted into opposite ends of brush base 104 at brush arm elbowsections 122 and 124. FIG. 3 is a side view of assembly 100 showinglongitudinal line E-E bifurcating the assembly along the length of brusharm 106. FIG. 4 shows a cross section of assembly 100 at line E-E. Asshown in FIG. 1, assembly 100 is inserted into motor cover 128 at brushbase attachment section 126, thereby fixing brush arms 106 and 108 tothe inside area of motor cover 128.

FIG. 1 also shows a conventional through-hole type capacitor 102 havingtwo electrically conductive metal wire legs 102 a and 102 b extendingdownward and outwardly from the body of the capacitor. In a conventionalmotor assembly using a capacitor in the electric input circuit forfiltering electromagnetic noises, wire legs 102 a and 102 b of capacitor102 are electrically connected to brush arms 106 and 108 at externalelectrical connections 118 and 120 by threading wire legs 102 a and 102b through holes 110 and 112, respectively, and soldering the wire legsto the external electrical contacts at holes 110 and 112 and thencutting off any residual metal wire to ensure fitment. FIG. 5 shows aconventional DC electric motor 130 including motor cover 128 attached tomotor housing 132 and rotor shaft 129 extending through opposite ends ofmotor 130. FIG. 5 also shows capacitor 102 soldered to externalelectrical contacts 118 and 120 at solder holes 110 and 112 inaccordance with the conventional assembly method. As shown in FIG. 5,under the conventional assembly method capacitor 102 is located outsidethe motor cover and motor housing.

This conventional design and assembly method entails a number ofproblems including, for example: (i) difficulty inserting the wire legsof the capacitor through small holes in the external electrical contactsof the brush arms before the capacitor can be soldered into place; (ii)difficulty soldering the wire legs to the external electrical contactsof the brush arms; and/or (iii) difficulty controlling the consistencyof the quality of the soldered connection. Also, the conventional designand assembly method locates the capacitor outside of the protectivemotor cover and motor housing, where the capacitor is more susceptibleto physical damage during assembly, installation and/or use.

FIG. 6 shows a prior art motor cover 200 for use in a miniature, DCelectric motor by Johnson Electric. The Johnson design shown in FIG. 6uses a chip capacitor 202 and choke coil 204 located in the motor coverto form an “L-C” circuit to suppress the electrical noise generated fromthe commutation between the two brushes and the commutator. As shown inFIG. 6, the chip capacitor in Johnson's design is located on one side ofthe motor cover opposite to the side where brush arms 206 and 208 arelocated.

Thus, it will be appreciated that there is a need in the art for a motorassembly design, and/or method of making the same, that overcomes someor all of these and/or other problems and/or that effectively providesfor DC electric motor input noise filtering using a simplified and costefficient manufacturing approach.

One aspect of certain exemplary embodiments relates to a simplifiedelectric motor design, and/or a method of making the same.

Another aspect of certain exemplary embodiments relates to a capacitorin an electric motor input circuit for filtering electromagnetic noises.

Still another aspect of certain exemplary embodiments relates to acapacitor supported or held between two brushes of a motor assembly andin a solderless electrical connection therewith.

In certain exemplary embodiments, a motor assembly for an electric motorincludes an electric motor having a motor cover, a brush base forholding two brush arms, and a chip capacitor having two terminal endswith the first terminal end in solderless surface contact with the firstbrush arm and the second terminal end in surface contact with the secondbrush arm.

In certain exemplary embodiments, a motor assembly for an electric motorincludes a brush holder, a chip capacitor, and two brush arms, with atleast one of said brush arms shaped to support or hold the capacitorbetween the two brush arms and in surface contact therewith.

In certain exemplary embodiments, a method for assembling a DC electricmotor including inserting two brush arms into a brush base at oppositesides of a hollow space provided in the brush base and inserting aceramic chip capacitor in the hollow space between the two brush armssuch that one terminal end of the capacitor is in surface contact withone of the brush arms and the other terminal end of the capacitor is insurface contact with the other brush arm.

These features, aspects, and advantages may be combined in any suitablecombination to realize yet further exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain features, aspects and advantages of the embodiments describedherein will be better understood from the following detaileddescription, including the appended drawings, in which:

FIG. 1 is an exploded view of a conventional motor cover and brush baseassembly including a through-hole type capacitor, a brush base, twobrush arms, and a motor cover;

FIG. 2 is a sectional view of a conventional brush base and brush armassembly including a brush base and two brush arms;

FIG. 3 is a side view of the brush base assembly of FIG. 2;

FIG. 4 is a cross-section view of the brush base assembly of FIG. 2;

FIG. 5 is a perspective view of a conventional DC electric motorincluding an exposed capacitor;

FIG. 6 is a sectional view of a prior art motor cover including a chipcapacitor, a coil and two brush arms;

FIG. 7 is a perspective view of an exemplary embodiment of a DC electricmotor of the new design and assembly method;

FIG. 8 is an exploded view of an exemplary embodiment of the new designand assembly method including a brush base, brush arms, a ceramic chipcapacitor, and a motor cover;

FIG. 9 is a side view of a brush base and brush arm assembly of FIG. 8;

FIG. 10 is a cross-section view of the brush base and brush arm assemblyof FIG. 9;

FIG. 11 is a sectional view of an exemplary embodiment of the brush baseand brush arm assembly of the new design and assembly method; and

FIG. 12 is a cross section view of the brush base and brush arm assemblyof FIG. 11.

DETAILED DESCRIPTION OF CERTAIN EXEMPLARY EMBODIMENTS

Referring now to the drawings, in which like reference numeralsdesignate similar parts throughout the various views, FIG. 7 shows anexemplary embodiment of a DC electric motor 300 of the new design andassembly method. DC electric motor 300 includes motor housing 302 andmotor cover 304, which together, among other things, protect theinterior components of the motor. Rotor shaft 305 extends throughopposite ends of motor 300. Also shown in FIG. 7 is the external surfaceof brush base 306 with external electric contacts 308 and 309 (havingholes 310 and 312, respectively) which preferably extend outwardly fromopposite ends of the brush base along an axis perpendicular to the axisof rotor shaft 305. While the embodiment shown in FIG. 7 has particularapplication to motorized toys, audio and video equipment, hand tools andother electrical motor-driven devices, vehicles or appliances, theinvention is not limited to these applications and can be used in anysuitable application.

FIG. 8 shows an exploded view of preferred brush base and brush armassembly 307 of motor 300. Assembly 307 includes chip capacitor 326,brush base 306 and brush arms 313 and 314, said brush arms having at oneend brushes 318 and 320, and at the other end external electric contacts308 and 309, respectively. Chip capacitor 326 may be any capacitorsuited for use as a filter for electromagnetic noise in an electricmotor input circuit. For example, chip capacitor 326 may be a multilayersurface mount ceramic capacitor constructed by screen printingalternative layers of internal metallic electrodes onto ceramicdielectric materials fired into a concrete monolithic body, thencompleted by application of metal to the terminal ends of the capacitorwhich are fired to permanently bond with the individual electrodes.Other capacitor types and/or firing techniques may be used in connectionwith different exemplary embodiments, as will be appreciated by one ofordinary skill in the art from the description herein. The particularand other characteristics of the chip capacitor are selected or adaptedto be suitable for the particular application in which the capacitor isused.

As shown in the exemplary embodiment of FIG. 8, brush arms 313 and 314are inserted into brush base 306 at elbow sections 322 and 324,respectively, with external contacts 308 and 309 extending outwardly inopposite directions from brush base 306. In the exemplary embodiment,chip capacitor 326 is inserted between brush arms 313 and 314 within ahollow, protective space (not shown) provided in brush base 306. Theterminal ends 328 and 330 of chip capacitor 326 are thereby positionedsuch that they are in surface contact with brush arms 313 and 314 atelbow sections 322 and 324, respectively, within said hollow spaceprovided in brush base 306. Brush arms 313 and 314 are preferably shapedat elbow sections 322 and 324 to bulge inwardly in the direction of chipcapacitor 326 located in the hollow space (not shown) provided in brushbase 306 in order to support or hold chip capacitor 326 within thehollow space and maintain surface contact with the terminal ends of thechip capacitor, thereby providing a solderless electrical connectionbetween the terminal ends of the chip capacitor and the brush arms. Aswill be appreciated by one skilled in the art, elbow sections 322 and324 of brush arms 313 and 314 may be shaped using any number of knownmethods, for example, by bending, stamping, or forging at least one ofthe brush arms such that tension is applied to the chip capacitorsufficient to support or hold the chip capacitor in place between brusharms 313 and 314 while maintaining sufficient surface contact with thebrush arms to provide a solderless electrical connection between brusharms 313 and 314 and terminal ends 328 and 330 of the capacitor,respectively. Moreover, brush arms 313 and 314 may comprise anadditional piece or pieces at one or both elbow sections 322 and 324adequate to supply sufficient tension to the chip capacitor in order tosupport or hold the chip capacitor in place between brush arms 313 and314 while maintaining sufficient surface contact with the brush arms toprovide a solderless electrical connection between brush arms 313 and314 and terminal ends 328 and 330 of the capacitor, respectively.

In the exemplary embodiment shown in FIG. 8, chip capacitor 326 issandwiched between motor cover 304 and brush base 306 within the hollowspace provided in brush base 306. However, various other embodiments maybe configured such that brush base 306 is an integral part of motorcover 304 and serves as a brush arm holder having a protective hollowspace for accepting and housing chip capacitor 326 and positioning thechip capacitor between brush arms 313 and 314 such that surface contactis maintained between the brush arms 313 and 314 and chip capacitorterminal ends 328 and 330, respectively, such that a solderlesselectrical connection is maintained between the capacitor and the brusharms.

FIG. 8 also includes motor cover 304 having a brush base attachmentsection 332 for attaching brush base and brush arm assembly 307 to motorcover 304. Preferably, brush base attachment section 332 is shaped toaccept brush base and brush arm assembly 307 and support or hold itfixably in place to facilitate attachment of the motor cover to themotor housing. In an exemplary embodiment, motor cover post 333 isprovided in motor cover 304 at brush arm attachment section 332 in orderto accept and fixably attach brush base 306 to motor cover 304 by liningup brush base attachment hole 334 with motor cover post 333 and pressingthe brush base and the motor cover together, such that post 333 isinserted into hole 334 thereby fixably attaching the brush base andbrush arm assembly 307 to motor cover 304 at brush base attachmentsection 332.

FIG. 9 shows a side view of brush base and brush arm assembly 307 withline E-E bifurcating brush arm 314. FIG. 10 is a cross-sectional view ofassembly 307 showing capacitor 326 located between brush arms 313 and314 at elbow sections 322 and 324 within the hollow space provided inbrush base 306. In the exemplary embodiment, chip capacitor 326 issupported or held in place by brush arms 313 and 314 at elbows 322 and324 such that terminal ends 328 and 330 of capacitor 326 are in surfacecontact with the brush arms at elbow sections 322 and 324, respectively.

FIG. 11 shows brush base and brush arm assembly 307 before insertion ofchip capacitor 326 in order to show the M-shaped protective hollow spaceprovided in brush base 306 for supporting or holding the capacitor. Aswill be appreciated by a person of ordinary skill in the art, the hollowspace could be one of a variety of hollow shapes located between brusharms 313 and 314 at elbow sections 322 and 324 suitable to provide aprotective housing for chip capacitor 326. FIG. 11 also showscross-sectional line C-C through said hollow space provided in brushbase 306. FIG. 12 is a cross-section view of FIG. 11 along line C-Cshowing the hollow space with chip capacitor 326 inserted between brusharm elbow sections 322 and 324. As shown in FIG. 12, terminal ends 328and 330 of chip capacitor 326 are in surface contact with the brush armsat elbow sections 322 and 324, respectively, thereby providing asolderless electrical contact between the brush arms and the capacitor.Also shown are exemplary shapes formed in the brush arms at elbowsections 322 and 324 which bulge inward toward the capacitor providingsufficient tension to support or hold the capacitor in place within thehollow space provided by brush base 306 such that a solderlesselectrical connection is maintained between the terminal ends of thecapacitor and the brush arms.

Primary benefits of certain exemplary embodiments of the new design andassembly method include: (i) lower assembly cost, including lower laborcosts; (ii) better fitment of motor assembly parts; (iii) fewer qualitycontrol problems with motor parts and assemblies; and/or (iii) betterprotection of the capacitor from physical damage. For example, theelimination of a soldered electrical connection between the capacitorand the brush arms provides several advantages. For example, because thebrush arms and the metal legs of a conventional capacitor are typicallymade of different metals such as, for example, copper in the former andiron in the latter, there may be a significant difference in the twometal's respective melting points (copper: 1,084° C.; iron: 1,536° C.).At too low of a temperature, it is difficult to solder the piecestogether at all. At higher temperatures, soldering is facilitated, butthe additional heat can lead to deformation of the brush arms and/orbrushes, thereby adversely affecting performance of the motor.Furthermore, the solder size and the location of the solder must beconstantly monitored and carefully controlled, as too large a soldersize or an improperly located solder may, for example, interfere withproper fitment of the motor cover onto the motor housing in the assemblyprocess. On the other hand, a solderless electrical connection betweenthe capacitor and the brush arms such as, for example the one shown inFIG. 8, helps to reduce the likelihood of occurrence of the problemstypically associated with a soldered electrical connection. Also, byusing a chip capacitor located within the hollow space of the brush base306, rather than a conventional capacitor with metal legs soldered tothe external electrical contacts of the brush arms and located outsidethe motor cover and motor housing, the capacitor is provided with aprotective housing which serves to reduce the risk of physical damage tothe capacitor during assembly, installation and/or use.

An exemplary embodiment of the improved assembly method includes, in noparticular order, inserting brush arms 313 and 314 at elbow sections 322and 324 into brush base 306 at opposite ends of the brush base. Themethod further includes inserting chip capacitor 326 into the hollowspace provided in brush base 306 and between brush arms 313 and 314 atelbow sections 322 and 324 such that terminal ends 328 and 330 of thecapacitor are in surface contact with elbow sections 322 and 324,respectively, forming brush base and brush arm assembly 307. The methodfurther includes lining up brush base attachment hole 334 with motorcover post 333 and pressing the brush base and the motor cover together,such that post 333 is inserted into hole 334 thereby fixably attachingthe brush base and brush arm assembly 307 to motor cover 304 at brushbase attachment section 332.

It is to be understood that the invention is not to be limited to thedisclosed embodiments, on the contrary, it is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1.-15. (canceled)
 16. A method for assembling a direct current electricmotor, the method comprising: inserting a first brush arm and a secondbrush arm into a brush base at opposite ends of a hollow space providedin said brush base; inserting a chip capacitor having two terminal endsinto the hollow space provided in said brush base; and positioning thecapacitor and the brush arms such that one terminal end of the capacitoris in surface contact with the first brush arm and the other terminalend of the capacitor is in surface contact with the second brush arm.17. A method according to claim 16, further including shaping at leastone of the brush arms to hold the capacitor in said hollow space.
 18. Amethod according to claim 16, further including inserting a surfacemount ceramic capacitor in said hollow space.
 19. A method according toclaim 16, further including making solderless electrical connectionsbetween the capacitor and said first and second brush arms.
 20. A methodaccording to claim 16, further including inserting the brush base into amotor cover.